ALEXANDRIAN OR HELLENISTIC PERIOD 



medes a century before, was studying the problems of 

 matter and putting his studies to practical application 

 through the invention of weird devices The man's 

 name was Ctesibius. We know scarcely more of him 

 than that he lived in Alexandria, probably in the first 

 half of the second century B.C. His antecedents, the 

 place and exact time of his birth and death, are quite 

 unknown. Neither are we quite certain as to the pre- 

 cise range of his studies or the exact number of his dis- 

 coveries. It appears that he had a pupil named Hero, 

 whose personality, unfortunately, is scarcely less ob- 

 scure than that of his master, but who wrote a book 

 through which the record of the master's inventions 

 was preserved to posterity. Hero, indeed, wrote sev- 

 eral books, though only one of them has been preserved. 

 The ones that are lost bear the following suggestive 

 titles: On the Construction of Slings; On the Construc- 

 tion of Missiles; On the Automaton; On the Method of 

 Lifting Heavy Bodies; On the Dioptric or Spying-tube. 

 The work that remains is called Pneumatics, and so 

 interesting a work it is as to make us doubly regret the 

 loss of its companion volumes. Had these other books 

 been preserved we should doubtless have a clearer in- 

 sight than is now possible into some at least of the 

 mechanical problems that exercised the minds of the 

 ancient philosophers. The book that remains is chiefly 

 concerned, as its name implies, with the study of gases, 

 or, rather, with the study of a single gas, this being, 

 of course, the air. But it tells us also of certain studies 

 in the dynamics of water that are most interesting, 

 and for the historian of science most important. 

 Unfortunately, the pupil of Ctesibius, whatever his 

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